A dietary based energetics model for bobcats (Lynx rufus) in a deep snow environment

Background/Question/Methods

Determining dietary niche in atypical environments and during times of limited resources can inform our understanding of the behavioral plasticity, prey switching ability, and potential for competitive interaction among sympatric congeners.  Winter diet and dietary niche breadth of bobcats (Lynx rufus) has not been investigated in Montana in a deep snow environment, where the Threatened Canada lynx (Lynx canadensis) is both sympatric and potentially better adapted ecologically and morphologically.  We tested the diet composition of a bobcat population to determine if bobcats in this region showed facultative specialization on snowshoe hares (Lepus americanus), the primary prey of the bobcat’s congener, Canada lynx.  Following dietary overlap analyses, we then developed energetics models based on average movement distances, body mass, and observed diet of bobcats to investigate if individual bobcats were able to maintain energy balance in this harsh winter environment.  Our main objectives were to (1) determine if bobcats were able to meet daily energy requirements on the observed diet, and (2) determine the conditions (movement distances and time spent active) for which bobcats would be unable to stay in energy balance on the observed winter diet.

Results/Conclusions

Bobcat scat and stomach samples showed that bobcats in this region consumed 5 major prey groups:  deer (Odocoileus spp.), snowshoe hares, red squirrels (Tamiasciurus hudsonicus), Cricetidae (rodents, subfamilies Neotominae and Arvicolinae), and Tetraoninae (grouse).  Diet of northwest Montana bobcats differed significantly from the diet of other bobcats in northern latitudes, with squirrels consumed more than expected, and deer and hares consumed less than expected.  Bobcat standardized niche breadth was 0.43, which did not overlap significantly with lynx in the western United States and Canada.  Bobcats in northwest Montana appear to depend on squirrels and other rodents in the winter and are not switching to snowshoe hares during this season.  Energetics modeling revealed that bobcats maintained long-term winter energy balance despite the reliance on small prey.  As we observed no over-winter starvation by bobcats, we assumed the model reflected conditions and parameters that bobcats are able to cope with in northwest Montana through a variety of physiological and behavioral adaptations.